Plasma Etched Catalytic Laminate with Traces and Vias

ABSTRACT

A circuit board is formed from a catalytic laminate having a resin rich surface with catalytic particles dispersed below a surface exclusion depth. The catalytic laminate is subjected to a drilling and blanket surface plasma etch operation to expose the catalytic particles, followed by an electroless plating operation which deposits a thin layer of conductive material on the surface. A photo-masking step follows to define circuit traces, after which an electro-plating deposition occurs, followed by a resist strip operation and a quick etch to remove electroless copper which was previously covered by photoresist.

FIELD OF THE INVENTION

The present invention relates to a catalytic laminate and its uses incircuit board fabrication. In particular, the laminate has propertieswhich provide for fine pitch circuit interconnects which can be formedon the surface of the catalytic laminate or in trenches to form circuitboard layers having planar surfaces with embedded or surface conductors.

BACKGROUND OF THE INVENTION

Prior art printed circuit boards (PCB) are formed using conductive metalinterconnects (known as “traces”) formed on a dielectric substrate,where each surface carrying conductors is known as a “layer”. Eachdielectric core has traces formed on one surface or on both surfaces,and by stacking several such dielectric cores having traces formed inthem interspersed with bare dielectric layers, and laminating themtogether under temperature and pressure, a multi-layer printed circuitmay be formed. The dielectric substrate comprises an epoxy resinembedded in a fiber matrix such as glass fiber woven into a cloth. Inone prior art fabrication method, copper is laminated onto the outersurfaces of a dielectric layer, the copper surfaces are patterned suchas with a photoresist or photo sensitive film to create masked andunmasked regions, and then etched to form a conductive trace layer onone or both sides of the core dielectric. A stack of dielectric coreswith conductive traces may then be laminated together to formmulti-layer boards, and any layer interconnects made with vias, whichare drilled holes plated with copper to form annular rings which provideconnectivity from one layer to another.

Printed circuit boards (PCB) are typically used to provide conductivetraces between various electronic components mounted on the PCB. Onetype of electronic component is a through-hole device which is mountedon the PCB by having leads positioned through one or more holes in thePCB, where the PCB hole includes a conductive annular ring pad on eachtrace connect layer, and the component lead is soldered to the annularring pad of the PCB hole. Through hole components have leads which tendto be difficult to align with the associated PCB mounting hole, butsurface mount technology (SMT) provides a preferable mounting system,where component leads are simply placed on the surface of a PCB pad andsoldered, which is preferred for PCB assembly because of the higherdensity and ease of mechanized assembly. Surface mount componentsrequire only surface mount pads on an outside finished PCB layer. Withina two layer or multi-layer PCB, interconnects of conductive traces fromone layer to another are accomplished using through-hole vias, where aconductive trace on one trace layer leads to a hole which is typicallydrilled through one or more dielectric layers of the PCB and plated withcopper or other conductive metal to complete the trace layer connection.A hole drilled through all dielectric layers is known as a thru-via, ahole drilled through an outer layer only (typically as part of thefabrication of the individual layer) is known as a micro-via, and a holedrilled through one or more inner layers is known as a blind via. Forany of these via types, the via is patterned to include an annular ringconductor region on opposite trace layers of the PCB, with the drilledhole lined with conductive material which connects the annular ringconductors on either side of the laminate or PCB.

The thickness of pre-patterned or post-patterned copper on a printedcircuit board laminate may be increased using electroplating, where thePCB or dielectric layer with traces is placed in an electrolytic bath,and a DC source is connected between a sacrificial anodic conductor(such as a copper rod) to an existing conductive layer of a PCB. Where apre-existing conductive copper layer is not present on a PCB tofacilitate electroplating, such as the case of bare dielectric materialor drilled via holes, a seed layer of copper must first be deposited.This is done using an electroless process with the assistance of a“seed” catalytic material (which enhances the deposition of a particularconductive material) which is deposited on the surface of thedielectric, and the board is then placed in an electroless bath. For acatalyst such as palladium and an electroless bath of copper, the copperions in solution deposit over the palladium until the surface is coveredsufficiently to provide uniform electrical conductivity, after which thecopper deposited using the electroless process provides a conductivescaffold for the subsequent addition of material using theelectroplating process. Electroplating is preferred for finishing theplating operation, as it has a faster deposition rate than theelectroless plating process.

As electronic assemblies increase in complexity, it is desired toincrease component densities on PCB assemblies, such as by using smallertrace widths (known as fine pitch traces) in conjunction withincreasingly dense integrated circuit (IC) lead patterns. One problem ofprior art surface mount PCB fabrication and assembly methods is thatbecause the traces are formed on the surface of the dielectric, theadhesion between copper trace and underlying laminate for narrowerconductor line widths (known as fine pitch traces) is reduced, causingthe fine pitch traces and component pads to separate (lift) during acomponent replacement operation, ruining the entire circuit boardassembly and expensive components on it. Another problem of fine pitchsurface traces is that when fabricating a multi-layer circuit board, theindividual trace layers are laminated together under pressure in anelevated temperature environment. During lamination, fine pitch tracestend to migrate laterally across the surface of the dielectric. In highspeed circuit design, it is desired to maintain a fixed impedancebetween traces, particularly for differential pair (edge coupled)transmission lines. This lateral migration of traces during laminationcauses the transmission line impedance of the finished PCB differentialpair to vary over the length of the trace, which causes reflections andlosses in the transmission line compared to one with fixed impedancecharacteristics resulting from constant spacing.

It is desired to utilize a catalytic pre-preg material which provides ablanket etched surface which exposes catalytic particles, thereafterforming traces using a combination of electroless plating to provide aconductive deposition layer, followed by electroless plating for formingtraces of desired thickness for fine trace linewidth and traceseparation. It is also desired to provide a catalytic pre-preg for usein printed circuit processing, where the catalytic pre-preg has acatalytic-free surface and where removal of the surface of the catalyticpre-preg exposes the catalytic particles for formation of traces inareas where surface material has been removed.

OBJECTS OF THE INVENTION

A first object of the invention is a catalytic pre-preg containingcatalytic particles, where the catalytic pre-preg conceals the catalyticparticles under a resin rich outer surface which does not expose thecatalytic particles unless the outer surface of the catalytic pre-preghas been removed, where the surface removal may be accomplished usingany of laser cutting, mechanical abrasion, mechanical cutting, chemicalor plasma etching, or any other means which removes the outer surface ofthe pre-preg and exposes the underlying catalytic particles below thesurface of the pre-preg, thereafter forming traces by drilling holes andperforming a blanket etch over the surface, electroplating the entiresurfaces, patterning the surface with a photoresist, electroplating thesurfaces without photoresist, stripping the photoresist and quicketching long enough to remove the exposed electroless plated copper.

A second object of the invention is a method for manufacture of acatalytic pre-preg which has a resin rich outer surface which does notcontain exposed catalytic particles and a catalyst rich layer below theresin rich outer surface, where the catalytic pre-preg is formed using aprocess having the steps:

a fiber infusion step wherein a fiber cloth is infused with a catalyticresin formed from blending a resin with catalytic particles;

a vacuum compression step performed at elevated temperature whereby theouter surfaces of the fiber cloth infused with catalytic resin aresubjected to externally applied pressure in an ambient vacuum conditionduring a temperature ramp time;

a gel point step whereby the applied pressure remains on the outersurfaces of the fiber cloth infused with catalytic resin to maintain aliquid/solid equilibrium for a duration of time sufficient for thecatalytic particles to be drawn away from the outside surfaces;

a dwell temp whereby an elevated temperature is applied to the laminatefor a dwell time duration at a gel point temperature;

a cooling step whereby the fiber cloth infused with catalytic resin iscooled into substantially planar sheets.

SUMMARY OF THE INVENTION

In a first embodiment of the invention, a catalytic pre-preg is formedby blending a resin, volatile solvent, and catalytic particles to form acatalytic resin mixture, infusing the catalytic resin into a fiberfabric such as woven glass fiber or other fabric to form an “A-Stage”catalytic pre-preg, baking the fiber and resin together at elevatedtemperature to remove most of the volatile solvent and form a partiallycured “B-Stage” catalytic pre-preg such as in sheet form, thereafterplacing the B-stage pre-preg into a lamination press, heating theB-stage pre-preg at a gel point such that the pre-preg is in aliquid/solid equilibrium, thereafter curing the pre-preg at an elevatedtemperature and pressure for a dwell time sufficient for the catalyticparticles to migrate away from the outer surfaces of the pre-preg and toform a finished “C-stage” pre-preg with a resin-rich surface which isfree from exposed surface catalytic particles. The mechanical removal ofthis resin rich surface thereby exposes the underlying catalyticparticles, forming a surface suitable for electroless plating usingcopper ions in solution, or any suitable electroless plating metal ionsin solution.

In a second embodiment of the invention, a single or multi-layer PCB isformed by patterning an exposed surface onto a catalytic pre-preg havinga resin rich surface which excludes catalytic particles from thesurface, where the catalytic particles are distributed below the resinrich surface and are not exposed. In a first step, the catalyticparticles are exposed by removing the surface of the material using anyremoval means, including laser ablation, plasma etching, chemicaletching, mechanical abrasion or cutting, using any of these techniqueswith or without a pattern mask. In a second step, the catalytic laminateis placed in an electroless plating bath, where the metal of theelectroless plating (such as Cu) is attracted to, and bonds to, theexposed catalytic particles (such as Pt) in the patterned regions wherethe resin rich surface has been removed. The second step continues untilthe electroless plating fills the sides and bottom of the patternedtrench with plated metal to the surrounding native surface level of thecatalytic laminate. In an optional third step, the surface of thepatterned trench is planarized, such as by polishing, grinding,machining, or etching, to match the level of the electroless platinglevel to the surrounding native surface of the catalytic laminate. In anoptional third or fourth step, soldermask is applied to cover regions ofthe catalytic laminate and regions of the patterned traces.

In a third embodiment of the invention, the catalytic pre-preg of thefirst embodiment has holes formed through drilling or ablation or othermeans of removing material to create an aperture in the catalyticpre-preg, the aperture adjacent to a pad region where the surface of thecatalytic pre-preg is removed adjacent to the aperture, thereby exposingunderlying catalytic particles of the catalytic pre-preg in the innersurfaces of the aperture and also the outer surfaces of the catalyticpre-preg, which is next plated into an electroless plating bath. Theresulting catalytic pre-preg thereafter forms a conductive surface tracewhich is electrically connected to a conductive via, which mayoptionally form a component mounting pad. The via may also include aconductive surface trace on the opposite side of the catalytic pre-preg,where the first surface trace, via, and second surface trace were allcreated in a single electroless plating step. After electroless plating,the outer surfaces of the catalytic laminate may be planarized such thatthe conductive traces are planar with the native surface of thecatalytic laminate, such that individual layers of catalytic laminatewith traces formed may be stacked and laminated into a multi-layer PCB.

In a fourth embodiment of the invention using a conventionalnon-catalytic pre-preg, a single or multi-layer PCB is formed by aprocess having a first step of applying a catalytic adhesive to one orboth sides of the non-catalytic pre-preg, where the catalytic adhesiveincludes a resin mixed with catalytic particles and forms a catalyticadhesive layer over the non-catalytic pre-preg. In a second step, thecatalytic pre-preg surface layer is selectively partially removed suchas by using a plasma cleaning or plasma etching process for a durationof time sufficient to expose the catalytic particles while leaving theunderlying adhesive resin which secures the catalytic particles to thenon-catalytic pre-preg. In a third step, the partially removed or etchedcatalytic adhesive is exposed to electroless plating using metal ions insolution which bind to the catalytic particles, which is performed untila substantially continuous conductive layer of metal is deposited. In afourth step, a pattern mask is applied which provides open areas wheretraces are desired. In a fifth step, the continuous conductive layer isused as an electrode for electroplating in a metallic bath such thatmetallic ions in solution electro-deposit onto the patterned exposedconductive layers formed in the third step electroless deposition. In asixth step, the pattern mask is stripped, and in a seventh step, a quicketch is performed for a sufficient time to remove the electrolessplating in previously unexposed areas under the pattern mask.

In a fifth embodiment of the invention, a conductive via is formed in anon-catalytic laminate by forming a first aperture in the non-catalyticlaminate, optionally adjacent to a first pad or second pad formed from aconductor on a first surface or second surface of the non-catalyticlaminate, filling the first aperture with a catalytic resin or catalyticadhesive, allowing the catalytic resin or adhesive to cure, drilling asecond hole in the first aperture which is smaller in diameter than theaperture, and electroless plating the second hole and surrounding pad,thereby forming a connection from the inner surface of the second holeto the first pad or second pad.

In a sixth embodiment of the invention, a non-catalytic laminate has acatalytic adhesive applied, the catalytic adhesive comprising a resinand catalytic particles, the catalytic adhesive having a thickness of atleast two times greater than the largest catalytic particles in theadhesive, the catalytic adhesive curing and developing a resin richsurface and an exclusion zone below the resin rich surface where thecatalytic particles are excluded, the removal of the resin rich surfaceproviding exposed catalytic particles suitable for electroless plating,the non-catalytic laminate optionally also having holes which may befilled with catalytic adhesive and drilled to provide exposed catalyticparticles for electroless plating of the drilled holes along withconductive traces formed by electroless copper deposition.

In a seventh embodiment of the invention, a catalytic laminate has acatalytic adhesive applied to at least one surface, the catalyticlaminate comprising a pre-preg with catalytic particles, the adhesivecomprising a resin and catalytic particles, the catalytic adhesive andcatalytic laminate drilled to form through holes, traces patterned onthe surface of the catalytic adhesive by removing the surface layer ofthe catalytic adhesive, thereafter forming traces by electroless platingon the patterned traces, thereafter planarizing the at least onesurface.

In an eighth embodiment of the invention, a circuit board is formed byblanket etching a catalytic pre-preg to expose catalytic particles belowan exclusion depth, drilling via holes, electroless plating the circuitboard, patterning the circuit board with a photoresist, electroplatingthe board to form traces on regions which are not coated withphotoresist, thereafter removing the photoresist, and quick etching theexposed electroless plated copper to form a circuit board with traces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic view of a process for forming a raw catalyticpre-preg.

FIG. 1B shows a vacuum lamination press for forming a finished catalyticpre-preg from a raw catalytic pre-preg.

FIG. 1C shows a vacuum lamination stage to for forming multiple layersof catalytic pre-preg during a lamination.

FIG. 2 shows processing times for a vacuum lamination step of FIG. 1.

FIG. 3 shows process steps for formation of a catalytic pre-preg.

FIG. 4 shows a plot of catalytic particle distribution in a pre-pregmaterial with respect to a section view of the pre-preg material.

FIG. 5A shows a section view of native catalytic pre-preg.

FIG. 5B shows a section view of catalytic pre-preg after a surfaceremoval step.

FIG. 5C shows a section view of catalytic pre-preg during an electrolessplating step during a time sequence.

FIG. 5D shows a section view of catalytic pre-preg after a surfacesmoothing step.

FIG. 5E shows a section view of catalytic pre-preg after a solder maskstep.

FIG. 5F shows a section view of a prior art etched copper trace on anon-catalytic pre-preg.

FIG. 6A shows a section view of a catalytic adhesive applied to anon-catalytic pre-preg.

FIG. 6B shows a section view of FIG. 6A after a plasma etch step.

FIG. 6C shows a section view of electroless plating over a pre-pregsubstrate.

FIG. 6D shows a section view of masking material patterned over apre-preg substrate.

FIG. 6E shows a section view of copper electroplate over a pre-pregsubstrate.

FIG. 6F shows a section view of copper electroplate after stripping amask.

FIG. 6G shows a section view of a pre-preg substrate after a quick etchto remove surface copper.

FIG. 7A shows a section view of a non-catalytic pre-preg with foillamination.

FIG. 7B shows a section view of an etched non-catalytic pre-preg afterpatterning.

FIG. 7C shows a section view of a non-catalytic pre-preg after a hole isdrilled.

FIG. 7D shows a section view of a non-catalytic pre-preg after filling ahole with catalytic filler.

FIG. 7E shows a section view of a non-catalytic pre-preg after drillingof a second annular hole.

FIG. 7F shows a section view of a non-catalytic pre-preg afterelectroless plating of an annular hole.

FIG. 7G shows a perspective transparent view of a via formed using theprocess of FIGS. 7A to 7F.

FIG. 8A shows a section view of a non-catalytic pre-preg laminate.

FIG. 8B shows FIG. 8A after application of a catalytic adhesive.

FIG. 8C shows FIG. 8B after a hole drill/punch operation.

FIG. 8D shows FIG. 8C after a surface removal operation.

FIG. 8E shows FIG. 8D after an electroless plating operation.

FIGS. 9A, 9B, 9C, 9D, and 9E show various stages of a section view of acatalytic adhesive applied over a catalytic laminate, which is drilled,etched, electroless plated, and planarized.

FIGS. 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H and 10I show various stagesof a section view of a catalytic laminate, which has traces formed onexposed catalytic surfaces.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows an example process for fabricating pre-preg (a matrix ofpre-impregnated fibers bound in resin). Many different materials may beused for the fibers of pre-preg, including woven glass-fiber cloth,carbon-fiber, or other fibers, and a variety of different materials maybe used for the resin, including epoxy resin, polyimide resin, cyanateester resin, PTFE (Teflon) blend resin, or other resins. One aspect ofthe invention is a printed circuit board laminate capable of supportingfine pitch conductive traces on the order of 1 mil (25 u), and while thedescription is drawn to the formation of copper traces using catalystsfor electroless copper formation, it is understood that the scope of theinvention may be extended to other metals suitable for electrolessplating and electro-plating. For electroless deposition of copper (Cu)channels, elemental palladium (Pd) is preferred as the catalyst,although selected periodic table transition metal elements, such asgroup 9 to 11 platinum (Pt), rhodium (Rh), iridium (Ir), nickel (Ni),gold (Au), silver (Ag), cobalt (Co), or copper (Cu), or other compoundsof these, including other metals such as iron (Fe), manganese (Mn),chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), tin (Sn),or mixtures or salts of the above, any of which may be used as catalyticparticles. The present candidate list is intended to be exemplar ratherthan comprehensive, it is known in the art that other catalysts forattracting copper ions may also be used. In one example of theinvention, the catalytic particles are homogeneous catalytic particles.In another example of the invention, the catalytic particles areinorganic particles or high temperature resistant plastic particleswhich are coated with a few angstrom thickness of catalytic metal,thereby forming heterogeneous catalytic particles having a thincatalytic outer surface encapsulating a non-catalytic inner particle.This formulation may be desirable for larger catalytic particles, suchas those on the order of 25 u in longest dimension. The heterogeneouscatalytic particle of this formulation can comprise an inorganic,organic, or inert filler such as silicon dioxide (SiO2), an inorganicclay such as Kaolin, or a high temperature plastic filler coated on thesurface with a catalyst such as palladium adsorbed onto the surface ofthe filler, such as by vapor deposition or chemical deposition. Only afew atomic layers of catalyst are required for the catalytic particle tohave desirable properties conducive to electroless plating.

In one example of forming heterogeneous catalytic particles, a bath offillers (organic or inorganic) is sorted by size to include particlesless than 25 u in size, these sorted inorganic particles are mixed intoan aqueous bath in a tank, agitated, and then a palladium salt such asPdCl (or any other catalyst such as a salt of silver of other catalyst)is introduced with an acid such as HCl, and with a reducing agent suchas hydrazine hydrate, the mixture thereby reducing metallic Pd whichcoats the inorganic particles provide a few angstroms of thickness of Pdcoated on the filler, thereby creating a heterogeneous catalyticparticle which has the catalytic property of a homogeneous Pd particlewith a greatly reduced volume requirement of Pd compared to usinghomogeneous Pd metallic particles. For extremely small catalyticparticles on the order of a few nm, however, homogeneous catalyticparticles (such as pure Pd) may be preferred.

Example inorganic fillers include clay minerals such as hydrous aluminumphyllosilicates, which may contain variable amounts of iron, magnesium,alkali metals, alkaline earths, and other cations. This family ofexample inorganic fillers includes silicon dioxide, aluminum silicate,kaolinite (Al₂Si₂O₅(OH)₄), polysilicate, or other clay minerals whichbelong to the kaolin or china clay family. Example organic fillersinclude PTFE (Teflon) and other polymers with high temperatureresistance.

Examples of palladium salts are: BrPd, CL₂Pd, Pd(CN)₂, I₂Pd,Pd(NO₃)₂*2H₂0, Pd(NO₃)₂, PdSO₄, Pd(NH₃) 4Br₂, Pd(NH₃)4Cl₂H₂O. Thecatalytic powder of the present invention may also contain a mixture ofheterogeneous catalytic particles (for example, catalytic materialscoated over inorganic filler particles), homogeneous catalytic particles(such as elemental palladium), as well as non-catalytic particles(selected from the family of inorganic fillers).

Among the catalysts, palladium is a preferred catalyst because ofcomparative economy, availability, and mechanical properties, but othercatalysts may be used.

FIG. 1A shows a roll of fabric cloth 102 such as woven glass fiber isfed through as set of rollers which guide the fabric into tank 108 whichis filled with an epoxy resin blended with catalytic particles and mixedwith a volatile liquid to reduce the viscosity, thereby forming anA-stage (liquid) pre-preg.

The resin may be a polyimide resin, a blend of epoxy and cyanide ester(which provides curing at elevated temperatures), or any other suitableresin formulation with selectable viscosity during coating andthermosetting properties after cooling. Fire retardants may be added,for example to comply with a flammability standard, or to be compatiblewith one of the standard FR series of pre-preg such as FR-4 or FR-10. Anadditional requirement for high speed electrical circuits is dielectricconstant ε (permittivity), which is often approximately 4 and governsthe characteristic impedance of a transmission line formed on thedielectric, and loss tangent δ, which is measure of frequency-dependentenergy absorption over a distance, whereby the loss tangent is a measureof how the dielectric interacts with high frequency electric fields toundesirably reduce signal amplitude by a calculable amount of dB per cmof transmission line length. The resin is blended with catalyticparticles which have been sorted for size. In one example formulation,the catalytic particles include at least one of: homogeneous catalyticparticles (metallic palladium), or heterogeneous catalytic particles(palladium coated over an inorganic particle or high temperatureplastic), and for either formulation, the catalytic particles preferablyhaving a maximum extent of less than 25 u and with 50% of the particlesby count sized between 12 u and 25 u, or the range 1-25 u, or smaller.These are example catalytic particle size embodiments not intended tolimit the scope of the invention. In one example embodiment, thecatalytic particles (either homogeneous or heterogeneous) are in thesize range 1 u-25 u. In another example of the invention, homogeneouscatalytic particles are formed by grinding metallic palladium intoparticles and passing the resultant particles through a sieve with amesh having 25 u rectangular openings. In another example, the catalyticresin mixture 106 is formed by blending homogeneous or heterogeneouscatalytic particles into the pre-preg resin by a ratio of weights, suchas the ratio of substantially 12% catalytic particles by weight to theweight of resin. The ratio by weight of catalytic particles in the resinmixture may alternatively be in the range of 8-16% of catalytic particleweight to the total weight of resin. It is understood that otherblending ratios may also be used, and it may be preferable to usesmaller particles. In one example of the invention, the catalyticparticle density is chosen to provide a mean distance between catalyticparticles on the order of 3 u-5 u.

After the fabric is immersed into the catalytic resin bath 106 withrollers 104, the catalytic resin impregnated cloth is guided to rollers110, which establish the thickness of the uncured liquid A-stagepre-preg 105 which also establishes the percentage of resin in theresin/glass+resin ratio. The A-stage pre-preg 105 is then passed througha baking oven 103 which drives out the organics and other volatilecompounds of the A-stage pre-preg and greatly reduces the liquidcontent, forming tack-free B-stage pre-preg 107 delivered by rollers111. In an example embodiment, oven 103 dries the volatile compoundsfrom an about 80% solvent ratio of A-stage pre-preg to less than about0.1% solvent ratio for B-stage pre-preg. The resulting B-stage pre-preg107 is provided to material handling 111 and can be cut into sheets forease of handling and storage, and is later placed into the laminationpress 126 of FIG. 1B which applies pressure across the surface of thesheets under vacuum, changing the temperature profile while the pre-pregcore is in the lamination press, following the temperature plot 202shown in FIG. 2. In one example of the invention, to create the resinrich surface, the pre-preg sheets positioned near the outer surfaces(which will later have the surface removed to expose the underlyingcatalytic particles) are selected to have greater than 65% resin, suchas Glass 106 (71% resin), Glass 1067, or Glass 1035 (65% resin), and theinner pre-preg sheets (which are not subject to surface removal) areselected to have less than 65% resin. Additionally, to reduce thelikelihood of fiberglass being present near the surface of the catalyticpre-preg, a woven fiberglass may be used with the inner pre-preg layersand a flat unwoven fiberglass may be used in the outer resin richpre-preg layers. The combination of resin-rich pre-preg and flat unwovenfiberglass on the outer surface layer results in an exclusion zone of0.7 mil (17 u) to 0.9 mil (23 u) between an outer surface and theencapsulated fiberglass. Glass styles 106, 1035, and 1067 are preferredfor use on the outer resin rich surface since the glass fiberthicknesses are smaller (1.3-1.4 mil/33-35 u) than the glass fiberthickness found in typical pre-preg sheets with greater than 65% resinused in the central regions of the laminate, such as glass style 2116,which has 3.7 mil (94 u) fibers. These values are given as examples, thesmallest glass fibers which are commercially available are expected tocontinue to reduce in diameter. The temperature vs. time plot 202 istailored in the present invention to cause the catalytic particles andfiberglass to migrate away from the outer surface of the laminate,repelled by the surface tension of the epoxy during a liquid state ofthe gel point temperature. After the cooling cycle of plot 202, thecured C-stage pre-preg sheets are offloaded 114. The process which formsthe cured C-stage pre-preg sheets may use single or multiple sheets offiber fabric to vary the finished thickness, which may vary from 2 mil(51 u) to 60 mil (1.5 mm).

FIG. 3 shows a flowchart for the process of making pre-preg laminatewith catalytic particles infused but excluded from the outer surface ofthe pre-preg. Step 302 is the blending of catalytic particles into theresin, often with an organic volatile added to lower the mixtureviscosity, which forms the catalytic resin 106 placed in reservoir 108.Step 304 is the infusion of catalytic resin into the fabric such asrollers 104 of FIG. 1 may provide to form A-stage pre-preg, and step 306is the initial rolling of catalytic resin infused fabric into B-stagepre-preg such as by rollers 110, step 307 is a baking step for removingorganic solvents to form B-stage pre-preg, and step 308 is the pressingof catalytic resin infused fabric 130 into sheets of catalytic C-stagepre-preg in lamination press 126, which follows the temperature cycle ofplot 202, with vacuum pump 128 evacuating chamber 124 throughout thelamination process to remove air bubbles from the epoxy and reduce anyair voids that may form in the epoxy. The cooled finished catalyticC-stage pre-preg sheets are cut and stored for later use.

The FIG. 2 plot 202 of temperature vs. time shows the temperatureprofile of the pre-preg in the lamination press 112, which is criticalfor the formation of a catalytic pre-preg which has surface property ofcatalytic particles being excluded from the outer resin rich surface,but which are present just below the outer resin rich surface. The resinis in liquid state in reservoir 108, and the pre-preg is in in anA-stage after the resin is impregnated into the fiberglass and passesthrough rollers 110. The pre-preg is in a B-stage after baking 103 wherethe volatile organics are baked off accompanied by an initial resinhardening, which converts the B-stage pre-preg into becomes C-stagepre-preg at the end of the lamination cycle, such as the cooling phaseof FIG. 2. The B-stage pre-preg is placed into the lamination press anda vacuum is pulled to prevent trapped air from forming betweenlamination layers. Heat is applied during a temperature ramp-up time 204to achieve a temperature and pressure determined pre-preg gel point 205for a duration on the order of 10-15 seconds (the gel point defined asthe state where the liquid and solid states are close to equilibriumwith each other), which is critical for the process of migrating thecatalytic particles away from the surface, after which the temperatureof the pre-preg is maintained at the dwell temperature and dwell time206 which may be in the range of 60-90 minutes, followed by a coolingcycle 208. The dwell temperature and gel point temperature are pressureand resin dependent, in the example range of 120 C (for epoxy) to 350 C(for Teflon/polyimide resins). Maintaining the pre-preg at the gel point205 for too short of a duration will result in the catalytic particlesor fiberglass being undesirably present at the surface of the finishedpre-preg.

FIG. 4 shows the resultant catalytic pre-preg 402 formed by the processof FIGS. 1, 2, and 3, where the catalytic particles 414 are distributeduniformly within the central region of pre-preg 402, but are not presentbelow a boundary region 408 below first surface 404, or below boundaryregion 410 below second surface 406. For the example particledistribution of particles smaller than 25 u, the catalytic particleboundary is typically 10-12 u below the surface (on the order of half ofthe particle size), accordingly this depth or greater of surfacematerial must be removed for the embedded catalytic particles to beavailable for electroless plating.

Prior art catalytic laminates have activated surfaces that must bemasked to prevent unwanted electroless plating on the activated surfaceof the catalytic laminate. By contrast, the catalytic laminate of thepresent invention excludes catalytic particles over the thickness extentfrom first surface 404 to first boundary 408, and from second surface406 to second boundary 410, providing the benefit that a separate masklayer preventing contact with the catalytic particles is not requiredfor electroless plating as it is in the prior art. Accordingly, removalof surface material from either first surface 404 to the depth ofboundary layer 408 or deeper, or removal of surface material from secondsurface 406 to second boundary 410, results in the exposure of catalyticmaterial which may be used for electroless plating. It is also desirablefor the process which provides the resin rich surface to also excludenot only catalyst, but the fiber fabric, as removal of the surface layerin subsequent steps which results in the exposure of fibers requiresadditional cleaning steps, accordingly it is preferred that the surfaceremoval be of resin only, so as to expose the underlying catalyticparticles. This is accomplished by using a combination of resin-richouter pre-preg layers and flat unwoven fiberglass layers having smallerdiameter fibers on the outside layers. An additional advantage offorming traces in channels using electroless plating is that the tracesare mechanically supported on three sides, which provides greatlyimproved trace adhesion to the dielectric laminate.

The sequence of FIGS. 5A to 5E show the process steps, identifyingvarious structures, but are not to scale, and provide only a simplifiedview of the process steps for understanding the invention. FIG. 5A showsa magnified cross section view of catalytic pre-preg 508 formed by theprocess of FIGS. 1, 2, and 3. Catalytic particles 502 may be in the sizerange of 25 u and smaller, in the present example they are shown in therange 12 u to 25 u for clarity. The catalytic particles may includeheterogeneous catalytic particles (organic or inorganic particles havinga catalytic surface coating) or homogeneous particles (catalytic metalparticles), as described previously. The first boundary 504 isapproximately 25 u below the first surface 506. The second surface 505and second surface boundary 503 on the opposite surface are shown forreference, but may be formed in the same manner as described for thesequence of FIGS. 5A to 5E. A drilled hole 511 which will provideconnectivity between traces on the first layer 506 and traces on thesecond layer 505 is also shown.

FIG. 5B shows the laminate of FIG. 5A with a channel 510 formed byremoval of the surface layer 506 in a region where a trace is desired.Pre-preg is also removed in an annular ring 513 of surrounding the via,at the same or different depth as the trace channel 510. The removal ofsurface material may be by laser ablation, where the temperature of thecatalytic pre-preg is instantly elevated until the catalytic pre-preg isvaporized, while leaving the surrounding pre-preg structurallyunchanged, leaving the catalytic particles exposed. It may be preferableto use a laser with a wavelength with a low reflectivity and highabsorption of this optical wavelength for the pre-preg material beingablated, such as ultraviolet (UV) wavelengths. Examples of such UVlasers are the UV excimer laser or yttrium-aluminum-garnet (YAG) laser,which are also good choices because of the narrow beam extent and highavailable power which for forming channels of precise mechanical depthand with well-defined sidewalls. An example laser may remove material ina 0.9-1.1 mil (23 u to 28 u) diameter width with a depth governed bylaser power and speed of movement across the surface. Another surfaceremoval technique for forming channel 510 and annular ring 513 is plasmaetching, which may be done locally or by preparing the surface with apatterned mask which excludes the plasma from the surface layers 506 or505, such as a dry film photoresist or other mask material which has alow etch rate compared to the etch rate of catalytic pre-preg. Thephotoresist thickness is typically chosen based on epoxy/photoresistetch selectivity (such that plasma etch to the desired depth of removalof the cured epoxy leaves sufficient photoresist at the end of theetch), or in the case of photoresist which is used as an electroplatemask, the thickness is chosen according to desired deposition thickness.Typical dry film thickness is in the range of 0.8-2.5 mil (20-64 u).Plasmas suitable for etching the resin rich surface include mixtures ofoxygen (O) and CF₄ plasmas, mixed with inert gasses such as nitrogen(N), or argon (Ar) may be added as carrier gasses for the reactivegases. A mask pattern may also be formed with a dry film mask, metalmask, or any other type of mask having apertures. Where a mechanicalmask is used, the etch resist may be applied using any ofphotolithography, screen printing, stenciling, squeegee, or any methodof application of etch resist. Another method for removal of the surfacelayer of pre-preg is mechanical grinding, such as a linear or rotationalcutting tool. In this example, the pre-preg may be secured in a vacuumplate chuck, and a rotating cutter (or fixed cutter with movable vacuumplate) may travel a pattern defining the traces such as defined by x,ycoordinate pairs of a Gerber format photofile. In another example ofremoving surface material, a water cutting tool may be used, where awater jet with abrasive particles entrained in the stream may impinge onthe surface, thereby removing material below the first boundary 504. Anyof these methods may be used separately or in combination to removesurface material and form channel 510 from pre-preg 508, preferably withthe channel extending below the first boundary 504. Accordingly, theminimum channel depth is the depth required to expose the underlyingcatalytic particles, which is a characteristic of the cured pre-preg. Asthe catalytic material is dispersed uniformly through the cured pre-pregbelow the exclusion boundary 504, the maximum channel depth is limitedby the depth of the woven fiber (such as fiberglass) fabric, which tendsto complicate channel cleaning, as the fibers may break off andre-deposit in channels intended for electroless plating, or otherwiseinterfere with subsequent process steps. Typical channel depths are 1mil (25 u) to 2 mil (70 u). The final step after removing the surfacematerial to form the channel 510 is to clean away any particles ofmaterial which were removed, which may be accomplished using ultrasoundcleaning, jets of water mixed with surfactant, or any other cleaningmeans which does not result in surface 506 material surrounding thechannel from being removed.

FIG. 5C shows contour plots for progress of electroless plating overtime, where the catalytic pre-preg of FIG. 5B is placed into anelectroless bath using a dissolved reducing agent to reduce the metalions to the metallic state on the catalytic pre-preg. One exampleelectroless copper bath formulation uses a mixture of Rochelle salt asthe complexing agent, copper sulfate as the copper metal source,formaldehyde as the reducing agent, and sodium hydroxide as a reactant.In this example, the tartrate (Rochelle salt) bath is preferred for easeof waste treatment; the Rochelle salt does not chelate as strongly asalternatives such as EDTA or quadrol. In this example, the tartrate(Rochelle salt) is the completing agent, copper sulfate is the metalsource, formaldehyde is the reducing agent, and sodium hydroxide is areactant. Other electroless plating formulations are possible, thisexample is given for reference. The electroless plating initially formsover the surfaces of the exposed catalytic particles, as shown in thehatch pattern 520 at time t1 and the matching hatch patterns in via 535.The copper deposition progresses as the electroless plating continues tothe hashed regions of deposition shown for subsequent times t2 522, t3524, and t4 526, at which time the deposition 526 may extend above thesurface 506 and the via 535 is also filled with copper.

A key advantage of electroless plating with channels etched in catalyticmaterial is that the electroless plating progresses on all three sidesat once, compared to electroplating which only progresses from thebottom (initially plated) layer.

FIG. 5D shows the result of a surface smoothing operation, where thefinished electroless plated trace 534 and via 535 are co-planar withsurface 532. Surface smoothing may be accomplished many different ways,for example using a 420 to 1200 grit abrasive applied on a planarsurface with mild pressure and linear or rotational agitation betweenthe board and planar surface to provide a grinding operation. Othermethods for planarizing the surface may be used, including milling ormachining using chemical processes, mechanical processes, or othermethods for forming a planar surface. FIG. 5E shows a soldermask layer536 which may be silkscreened over the trace 534 for isolation andprotection, such as a finished outer layer of a multi-layer board.

FIG. 5F shows a prior art etched copper trace for comparison purposes.Trace 554 is formed using a prior art subtractive etching process, wheretrace 554 is what remains after etching the rest of the copper which waspresent on a surface layer on non-catalytic pre-preg 550. The copperouter layer was patterned with a photoresist such as dry film andsubsequently surface etched, which creates the trapezoidal sectionprofile of trace 554 because the top of the trace experiences greaterlateral etching than the bottom of the trace adjacent to thenon-catalytic pre-preg 550. Another advantage of an additive process ofthe present invention is that for traces formed using a prior artprocess which etches all of the copper except the desired trace copper,surface contaminates on the surface cause adjacent trace shorting, as acopper bridge remains where the contamination was present on the surfaceof the copper, which does not occur in additive electroless plating ofthe present invention. For comparison with figure of the presentinvention, soldermask 552 is also shown. As seen in the figure, trace554 is only supported by adhesion to substrate 550, whereas FIG. 5Etrace 534 is supported on three sides, and is locked into its associatedchannel in the catalytic pre-preg 508.

FIGS. 6A to 6G show another embodiment of the invention usingnon-catalyst pre-preg 602, which may be a conventional pre-preg whichdoes not contain catalytic particles. In this example of FIG. 6A, viahole 603 is first punched or drilled into the non-catalytic pre-preg602. A catalytic adhesive is formulated by mixing a resin and catalyticparticles, which may be in the same proportions and manner as thecatalytic resin previous described (although it may have a higherviscosity for certain surface coating applications such as by squeegee),with the primary distinction being that the catalytic adhesive isapplied to a (typically) non-catalytic substrate, although it may alsobe applied to a catalytic substrate. For use in a catalytic adhesive,the catalytic particles are agitated until sufficiently wetted such thatthe catalytic adhesive 604 ensures that the catalytic particles 606 arenot exposed until a subsequent surface coating 604 removal operationsuch as the plasma clean of FIG. 6B. In the present example, thecatalytic resin is sprayed or squeegeed onto the surface ofnon-catalytic pre-preg 602 and into the via hole 603, as shown in FIG.6A. The catalytic adhesive comprises a resin 604 containing adistribution of catalytic particles 604, such as palladium particlessmaller than 25 u, or, in one example of the invention, with 50% of theparticles by number falling in the range of 12-25 u in longest particledimension, or with a range of particles from 1-25 u as possibleexamples. The catalytic adhesive may be formed as was previouslydescribed for the catalytic resin using the ratio of 8-16% catalystweight to resin weight, with 12% the preferred value. The resultingcatalytic adhesive may be applied to the non-catalytic substrate andboth baked to cure the catalytic adhesive to the non-catalytic pre-pregsubstrate 602. In one application method, the catalytic adhesive isapplied to the leading edge of a mechanized squeegee comprising aflexible blade carrying the catalytic adhesive and passing over thesurface of non-catalytic laminate, with the pressure and spacing betweenthe flexible blade and the non-catalytic laminate adjusted such that anydrilled holes are filled with catalytic laminate and a desired thicknessof catalytic laminate is uniformly disposed on the surface of thenon-catalytic laminate in a single pass of the squeegee. A typicalcatalytic adhesive thickness is 12-75 u thick. The catalytic adhesivethickness should be at least 2× thicker than the largest catalyticparticles, to ensure that the catalytic particle remains below thesurface of the catalytic adhesive.

The surface of FIG. 6A is next subjected to a plasma clean step, whichstrips the resin from regions above the catalytic particles and thesurface of the non-catalytic resin, leaving the catalytic particles 606adhered to the surface of the non-catalytic pre-preg 602 as shown inFIG. 6B. FIG. 6C shows the result of placing the plasma cleaned surfaceof FIG. 6B into an electroless plating bath, which is done for asufficient length of time to form a thin but continuous coat ofelectroless copper deposition 608, which initially forms over catalyticparticles 606 and spreads across the top surface. FIG. 6D shows theaddition of a pattern mask 610 over the electroless layer 608. Since anelectroless layer now covers the surface of non-catalytic pre-preg 602,an electroplate operation may occur next to plate additional copper ontothe exposed patterned areas, shown as trace 612 of FIG. 6E, which maydeposit copper 612 to a level below or above mask 610. A mask stripoperation is shown in FIG. 6F, which removes pattern mask 610, leavingcopper trace 612 and electroless copper layer 608. FIG. 6G shows theresults of a quick etch, which removes the thin layer of electrolesscopper 608 and an equal amount of the surface of trace 612, leavingbehind a trace comprising a homogeneous trace comprising electroplatedcopper 612 and the underlying electroless copper deposition 608, therebyproviding conductive circuit traces.

FIGS. 10A, 10B, 10C, 10D, 10D, 10E, 10F, 10G, 10H and 10I show a seriesof steps which may be performed on the catalytic laminate previouslydescribed in FIG. 4, having catalytic particles 414 distributedthroughout the catalytic laminate and having a catalytic particleexclusion depth 418 below surfaces 404 and 406 such that electrolessplating does not occur unless a surfaces 406 or 404 is removed to belowthe exclusion depth 418, thereby exposing catalytic particles.

FIG. 10A shows related associated pre-preg 1006 with external surfaces1004 and 1008 which are free of catalytic particles until the externalsurfaces are removed to the depth 1002 and 1010, respectively,sufficient to expose the underlying catalytic particles below theexclusion depth.

FIG. 10B shows example via or through hole 1012, which, when drilled,expose catalytic particles on inner surfaces 1014 of drilled hole 1012.

FIG. 10C shows the catalytic laminate 1006 after blanket etching theentire outside surfaces of the catalytic laminate 1006 to below theexclusion depth, thereby creating external surfaces 1018 which havecatalytic particles exposed. Original pre-etched catalytic laminatesurfaces 1016 are shown for reference. The order of operation fordrilling of holes/vias 1012 of FIG. 10B and external surface blanketetch of FIG. 10C may be performed in any order. The blanket etch maypreferably be performed using a reactive plasma, a chemical etchant,although laser cutting, waterjet cutting, mechanical abrasion,mechanical cutting, or any other means which uniformly etches the outersurface of the pre-preg and exposes the underlying catalytic particlesbelow the surface and into the exclusion depth may be used. The step ofFIG. 10C is performed without any pattern mask of the previous catalyticlaminate etching operations, as the objective is to remove theresin-rich surface to below the exclusion depth to expose catalyticparticles throughout the surface of the catalytic laminate 1006.

Deposition of surface conductors such as copper may be performed on asurface using two different plating techniques. In a first electrolessplating technique, a dielectric layer 1006 with exposed catalyticparticles such as palladium is immersed into a bath containing metalions such as copper. The rate of electroless deposition of metalliccopper onto a catalytic surface is slower than the rate ofelectro-plating deposition of metallic copper, but the electrolessplating occurs on all surfaces which have exposed catalytic particles,and also on surfaces which have copper. Electro-plating requires auniform conductive surface, hence electroless plating is used as apre-cursor to electro-plating. Electro-plating also requires an externalvoltage source, resulting in a faster rate of copper deposition thanelectroless deposition. A sacrificial copper anode having a positivevoltage is placed into an electrolyte bath, with a conductive surface tobe plated connected to a negative voltage. The anodic copper migrates asmetal ions from the anode and pass through the electrolyte to thecathodic surface, where the metal ions deposit. In the present example,the cathodic surface is the PCB needing copper plating. Electroplatingrequires that all surfaces have a common potential, which is typicallyaccomplished using a copper foil or an electroless plating step on adielectric surface having exposed catalytic particles until continuouselectrical conductivity across the entire board allows for the board tobe used as a cathode, as required for an anodic copper source.

FIG. 10D shows the completion of an electroless plating step, where thedrilled and surface-surface-etched catalytic laminate 1006 is placed inan electroless bath of metal ions (typically copper), which deposit ontothe external surfaces of the laminate 1018 as well as the inside of thedrilled holes 1014 of FIG. 10C to produce the continuously conductivesurface 1020, which is required for a subsequent electroplatingoperation. The thickness of electroless copper 1020 should be theminimal thickness required to assure continuous coverage for successfulelectroplating, and is typically on the order of 0.15 mil.

FIG. 10E shows the subsequent step of applying a patterned photoresist1024 over the previously applied electroless copper 1020, with thephotoresist 1024 covering all areas other than those where traces orannular conductors around drilled holes or vias 1012 are required. Thepatterned photoresist 1024 has the effect of isolating the patternedareas from subsequent electroplating.

FIG. 10F shows the subsequent step of electroplating copper 1022 overthe electroless copper 1020, which is used as an electrode in theelectroplating operation. The electroplating thickness 1022 may be ofany thickness, preferably less than the thickness of the resist 1024,and more than 1×, or preferably 2× or more of the thickness of theelectroless metal deposition 1020.

FIG. 10G shows a subsequent step of stripping the resist 1024 of FIG.10F, thereby exposing the originally applied thin electroless copperregions 1026. Preferably, the thickness of electroplated copper 1022 isgreater than the thickness of electroless copper 1020, such that thequick etch step of FIG. 10H preferentially removes exposed electrolesscopper regions 1026, and leaves virtually all of the electroplatedcopper 1022.

FIG. 10I shows the completed process. The boundaries between electrolesscopper 1020 and electroplated copper 1022 were presented previously forclarity in understanding the invention and processing steps. Aselectroplated copper 1022 deposits on exposed electroless copper 1020during the step of FIG. 10F, the resulting through hole plating aroundhole 1012 and traces 1020/1022 of FIG. 10I are continuous copper, asshown.

The series of FIGS. 7A to 7G show section views for a series of stepsfor forming a via in a conventional non-catalytic pre-preg 702 withupper foil lamination 704 and lower foil lamination 706. FIG. 7G shows aperspective view of the finished via, whereas FIGS. 7A to 7F are sectionviews through A-A of FIG. 7G at the end of various intermediateprocessing steps.

FIG. 7B shows a section view of the upper layer 704 and lower layer 706after patterning, where the trace 704 is to be connected to trace 706 onthe opposite surface of the non-catalyst dielectric 702. FIG. 7B shows avia hole 708, which may be formed by punching or drilling, the hole 708is positioned in the center of the annular ring of a pad 716 formed bythe upper trace 704 and a pad 718 formed by lower trace 706. FIG. 7Dshows a catalytic filler 710 such as a formulation for plugged vias withcatalytic particles. The catalytic filler 710 is typically a thickfluid, with a viscosity in the range of 70,000-80,000 centipoise (cP),which is placed in the via aperture 708 of FIG. 7C, and FIG. 7E shows asecondary hole 712 which is drilled in the catalytic filler 710, whichexposes the catalytic filler particles which are present in catalyticfiller 710, thereby making the catalyst available for electrolessplating operations. An electroless copper deposition step follows, andthe electroless copper Cu++forms a conductive deposition layer 714 overthe top trace 704, annular ring top pad 716, through secondary hole 712with catalytic particles exposed, over lower pad 718, and over lowertrace 706, which completes the electrical circuit from upper trace 704to lower trace 704 through via structure 710/714. As is clear to oneskilled in the art, although an annular ring conductor is shown on eachconnecting surface, it is possible for the trace to connect directlyinto the via with or without an annular ring.

FIG. 8A shows another method for electroless plating of traces onto alaminate, using a non-catalytic substrate or pre-preg 802, with optionalhole 804 drilled or punched for layer to layer connectivity. FIG. 8Bshows the application of catalytic adhesive 806, such as with asqueegee, screen printing, a stencil, or any other methods as previouslydescribed for FIG. 6A. Hole 804 is also filled with catalytic adhesive806 in this coating operation. FIG. 8C shows secondary drilling 808 inthe annular ring of hole 804, which activates the catalytic adhesive 806in the drilled hole 808 by exposing the catalytic particles. FIG. 8Dshows the removal 814 of surface layer 806 sufficient to expose thecatalytic particles for forming electroless plated conductive traces,pads, and vias. FIG. 8E shows the completion of electroless plating,with copper 816 plated onto the catalytic adhesive which has beendrilled, etched, or otherwise removed. Planarization may optionally beperformed, or soldermask applied, as was described for FIG. 5D. Incertain applications such as high frequency applications wheredielectric loss tangent is critical, it may be desirable to useheterogeneous mixtures of non-catalytic laminate 802, such as PTFE, witha resin based catalytic laminate. In this case, it may be necessary toroughen the surface of a non-catalytic laminate 802 such as PTFE usingplasma etching, chemical etching, or other methods known in the priorart for breaking long chain polymer molecules, thereby providing betteradhesion for the catalytic adhesive at the catalytic adhesive/PTFEboundary. In one example of the invention, the PTFE non-catalyticsubstrate 802 is homogeneous PTFE, in another example it is a laminate,and in either case, the substrate 802 may or may not include fiber (suchas glass fiber) reinforcement.

A variant of the laminate structure of FIGS. 8A through 8E is shown inFIGS. 9A to 9E, with the use of catalytic adhesive 906 over a catalyticlaminate 902. There are several advantages to this approach. Oneadvantage is the application of catalytic adhesive 906 does not requirethe through holes 908 be pre-drilled prior to application of catalyticadhesive as in 804 of FIG. 8A. Another advantage is that the resin richsurface can be formed by the catalytic adhesive 906 rather than thecatalytic substrate 904, so that the catalytic particles of substrate902 need not have an exclusion zone near the surface as was shown inFIG. 4, as this is now provided by the catalytic adhesive 906 applied toone or both sides of the substrate 902. FIG. 9C shows a section viewafter hole 908 is drilled, step 9D shows the surface removal 914, andFIG. 9E shows the electroless plating 916 using the previously describedmethods.

The preceding description is only to provide examples of the inventionfor understanding the underlying mechanisms and structures used, and isnot intended to limit the scope of the invention to only the particularmethods or structures shown. For example, the sequences of FIGS. 5A to5E and 6A to 6G show a single sided construction with the trace channelscut on first surface only, whereas the same structures and methods canbe applied to the second surface 505 without loss of generality, as theelectroless plating step can be applied to channels or exposed catalyston both sides of the board in a single step. Additionally, layersfabricated as in FIGS. 5A to 5E, 6A to 6G, 8A to 8E, 9A to 9E, 10A to10I, and vias of FIG. 7A to 7F can be formed on individual layers whichare subsequently laminated together into a single board with mixedlayers of catalytic pre-preg and non-catalytic pre-preg, and the scopeof claims related to “multilayer PCB” are to be interpreted to includesuch constructions. Similarly, although the trace structure and viastructures of FIGS. 5A to 5E, 6A to 6G, 8A to 8E, and 7A to 7F are shownin combination as they would normally occur on a PCB, these examples areonly for illustration, and are not intended to limit the invention tothese constructions. For example, a mounting hole for a through holecomponent with no electrical connection could be formed without aconnecting trace or annular ring according to the novel aspects of theprocess.

In the present specification, “approximately” is understood to mean lessthan a factor of 4 greater or smaller, “substantially” is understood tomean less than a factor of 2 greater or smaller. “Order of magnitude” ofa value includes the range from 0.1 times the value to 10 times thevalue.

Certain post-processing operations are not shown which are generic toprinted circuit board manufacturing, and may be performed using priorart methods on boards produced according to the novel process. Suchoperations include tin plating for improved solder flow, gold flash forimproved conductivity and reduced corrosion, soldermask operations,silkscreening information on the board (part number, referencedesignators, etc.), scoring the finished board or providing breakawaytabs, etc. Certain of these operations may produce improved results whenperformed on planarized boards of certain aspect of the presentinvention. For example, silkscreened lettering over traces or viastraditionally breaks up because of trace and via thickness over theboard surface, whereas these operations would provide superior resultson a planarized surface.

We claim: 1) A process for forming conductive traces on a catalyticlaminate, the catalytic laminate having a resin rich surface withinsufficient density of catalytic particles for surface electrolessplating, the catalytic laminate having catalytic particles dispersedbelow a catalytic particle exclusion depth sufficient for electrolessplating when exposed, the process comprising: drilling holes in thecatalytic laminate; etching the external surfaces of the catalyticlaminate until the catalytic particles are exposed; electroless platingthe catalytic laminate until a conductive metal is plated on theexternal surfaces and also inside the drilled holes; applying a patternmask to the external surfaces of the catalytic laminate; electrolessplating the external surfaces of the catalytic laminate; stripping thepattern mask; quick etching the circuit board sufficient to remove anypreviously masked electroless conductive metal. 2) The process of claim1 where the electroless plating and the electroplating deposit copper.3) The process of claim 1 where the electroplate deposition thickness isgreater than the thickness of the electroless deposition. 4) The processof claim 1 where the pattern mask is dry film. 5) The process of claim 1where the pattern mask is liquid photoresist. 6) The process of claim 1where plasma etching the external surfaces uses at least one of: areactive plasma, a chemical etchant, laser cutting, waterjet cutting,mechanical abrasion, or mechanical cutting. 7) The process of claim 1where said exclusion depth is less than 25 u. 8) The catalytic laminateof claim 1 where said catalytic particles are heterogeneous. 9) Thecatalytic laminate of claim 8 where said catalytic particle comprises afiller coated with a catalyst. 10) The catalytic laminate of claim 9where said filler is at least one of: a clay mineral, a hydrous aluminumphyllosilicate, silicon dioxide, kaolinite, polysilicate, a member ofthe kaolin or china clay family, or a high temperature plastic. 11) Thecatalytic laminate of claim 9 where said particle size is on the orderof 3 u or less than 3 u. 12) The catalytic laminate of claim 9 where theratio of said catalytic particles to said resin by weight is in therange 8% to 16%. 13) The catalytic laminate of claim 9 where saidcatalytic particle is silicon dioxide or kaolin coated with a catalyticmaterial. 14) The catalytic laminate of claim 9 where said catalyst ispalladium. 15) The catalytic laminate of claim 9 where said catalyst isat least one of: palladium (Pd), platinum (Pt), rhodium (Rh), iridium(Ir), nickel (Ni), gold (Au), silver (Ag), cobalt (Co), or copper (Cu),or other compounds or salts thereof. 16) The catalytic laminate of claim1 where said catalytic particles are homogeneous. 17) The catalyticlaminate of claim 16 where said catalyst is palladium. 18) The catalyticlaminate of claim 16 where said catalyst is at least one of: palladium(Pd), platinum (Pt), rhodium (Rh), iridium (Ir), nickel (Ni), gold (Au),silver (Ag), cobalt (Co), or copper (Cu), or other compounds or saltsthereof. 19) The catalytic laminate of claim 16 where the majority ofsaid catalytic particles have a size smaller than 25 u.